Project Summary The increasing prevalence of antimicrobial resistance (AMR) to the majority of existing antibiotics has generated a pressing global healthcare crisis. Certain highly resistant bacteria have acquired multiple mechanisms against all available antibiotics. New therapeutic formats that can overcome AMR are therefore in urgent need, and detailed understanding of their action is essential to combat bacterial resistance. Certain metal ions, such as AuI is known to be toxic to bacteria. Recent studies have shown that auranofin, a AuI-based drug against rheumatoid arthritis, displays potent antibacterial activity. If large amounts of AuI can be delivered to bacteria in a sustained manner, selectively driven by interactions with bacterial receptors, this would greatly enhance the antimicrobial efficacy owing to the increased and prolong local concentration AuI at or within the microorganisms. Consequently, the overall objective of this project is to develop and explore new antimicrobial agents, designed to result in targeted generation of AuI for bacterial cell death. We hypothesize that glycosylated and phosphine-coordinated, atomically-precise gold nanoclusters (AuNCs) can be selectively and multivalently addressed to specific bacteria, and thereby release large quantities of AuI at or within the cells for efficient antibacterial action. We also hypothesize that a judicial choice of phosphine coordination to the AuNCs can fine-tune the stability of the clusters, whereby a controlled and sustained AuI release can be achieved. The approach is innovative because glycosylated, atomically-precise gold nanoclusters represent a new class of antimicrobial agents through specific and multivalent bacterial targeting, and sustained release. The project is significant because it represents a new way to overcome AMR, and the work will contribute our fundamental understanding regarding the antimicrobial action of ultrasmall gold clusters. In Aim 1 of this project, we will synthesize atomically-precise gold clusters, functionalized with specific carbohydrate structures for selective targeting to bacteria. We anticipate that ultrasmall, well-defined, glycosylated AuNCs can serve as metastable delivery vehicles for antimicrobial AuI ions, through controlled disintegration and oxidation at or within bacterial cells. In Aim 2, the activity and antimicrobial mechanism of the glycosylated AuNCs will be studied with all classes of bacteria.